US3371240A - Frame type electrodes for electron discharge devices - Google Patents

Description

H. L. ORMSBY Feb. 27, 1968 FRAME TYPE ELECTRODES FOP. ELECTRON DISCHARGE DEVICES Y Filed Jun 29, 1965 FIG.

INVENTOR WITNESSES y m H m m m A m United States Patent Ofitice FRAME TYPE ELECTRODES FOR ELECTRON DISCHARGE DEVICES Harry L. Ormsby, Bath, N.Y., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed June 29, 1965, Ser. No. 478,008 5 Claims. (Cl. 313-350) ABSTRACT OF THE DISCLOSURE This invention relates to frame type electrodes for electron discharge devices and includes in one illustrative embodiment a pair of side rods between which are supported a plurality of lateral grid wires, and first and second cross straps disposed upon opposite sides at either end of the pair of side rods. The first and second cross straps are made of a substantially pure molybdenum which has been partially crystallized to an extent in the range of 20 to 80% in order to enable the cross strap to be welded to the side rods without producing an unduly brittle weld.

This invention relates to improved electron discharge devices, and in particular to improved grid structures for such devices.

In those applications where electron discharge devices are being operated at high frequencies and/ or at low noise levels, the spacing between a cathode element and a lateral grid wire of a control or first grid electrode of this device must be made smaller and with greater precision than in other electron discharge devices. If the spacing between the cathode element and the grid electrode is not accurately controlled, a great difference in the performance of similarly designed electron discharge devices will be -btaind when produced by mass production methods. The transconductance of such devices in general varies as a function of the spacing between the lateral grid wires of the control grid element and the surface of the cathode element; therefore, this spacing should be made as small as possible and must be accurately set if a product having improved, uniform characteristics is to be mass produced.

Another difiiculty in the production of high performance, electron discharge devices results from the necessity of providing grid elements having a greater number of turns per inch of the lateral grid wire. In the ordinary type of grid element structure, there are no means to establish an accurate and rigid spacing between the side support rods upon which the lateral grid wire is suspended. Also, as a greater number of turns per inch of lateral grid wire is used, it is necessary to reduce the diameter of the lateral grid wire to a value as low as .3 to .5 mil. As the diameter of the lateral grid wire decreases and as the number of turns of the lateral grid wire increases, the tension with which the lateral grid wire is wound about the side support rods becomes great enough to physically bend the side rods. Further, as the diameter of the lateral grid wire decreases, the strength of the lateral grid wire will become insufficient to support the side rods to which the grid wire is secured. As a result, the shape and the dimensions of the finished grid element tend to become distorted, which condition will make it difficult if not impossible to provide the desired uniform cathode to grid spacing.

A possible solution of this problem has been the utilization of a frame type support structure upon which the fine, lateral grid wire may be suspended. Typically, such frame structures consist of two side support rods which are interconnected rigidly by a plurality of cross members or straps. Grid structures as descibed above may be fomed by stampins: out a unitary member or by welding the individual straps to the side support rods. In the particular case 3,371,240 Patented F eb. 27, 1968 where the straps are welded to the support rods, it

is a normal practice to secure a pair of straps at both ends of the side support rods with each strap of the pair welded on opposing sides of the side support rods.

It would be desirable to eliminate two of the support straps and secure by welding two straps one at either end of the support rods. Such a grid electrode structure has been described in a copending application, entitled Assembly of Electrodes with Aligned Grid Wires for Electron Discharge Devices, by Goliardo Miale and Anton Van Der Jagt, Ser. No. 438,272, and assigned to the assignee of this invention. More specifically, the grid structure of this copending application comprises a pair of side support rods, a pair of support straps disposed on one side of and secured at either end of the side support rods, and a plurality of lateral grid wires disposed and suspended about the side support rods. However, problems have arisen with this grid structure when it was attempted to apply a high number of turns per inch of lateral grid wire. Specifically, it was found that the side support rods had a tendency to rotate and thus to bow inwardly under the tension exerted by the winding of the lateral grid wire. In order to overcome this defect, the pair of cross straps may be disposed on opposing or alternate sides and secured at each end of the side rods. In this manner, the grid structure is able to resist to a greater degree the twisting forces as applied by the winding of the lateral grid wire. However, it has been discovered that even with this improved structure that many of the grid electrodes tend to break either during the winding process or after they have been incorporated in the envelope of the electron discharge device. Typically, grid electrodes are made of a molybdenum material which tends when welded to completely recrystallize. Thus, there appears a specific area of weakness where the support cross strap is welded to the side rod and it is in this region that the grid electrode structure may break either during its manufacturing or in later use.

Accordingly, it is the general object of this invention to provide a new and improved electron discharge device.

It is another object of this invention to provide an improved elect-rode structure for an electron discharge device having a rigid structure which will withstand the winding of a lateral grid wire without fracturing.

It is a further object of this invention to provide a new and improved electron discharge device having therein an electrode structure presenting a reduced capacitive effect with its associated electrodes.

It is a further object of this invention to provide a new and improved electrode grid structure which may be manufactured at significantly reduced cost.

It is a still further object of this invention to provide a new and improved electrode grid structure wherein the joints between the members thereof is structurally strong and not subject to fracture.

Briefly, the present invention accomplishes the abovecited objects by providing an improved electron discharge device, wherein there is incorporated an electrode structure having a pair of side support rods supported and suspended from each other by two cross straps one of which is disposed at either end of and secured as by welding on alternate sides of said side support rods. More specifically, the cross straps are made of a substantially pure molybdenum which has been partially crystallized to a degree not exceeding and not less than 20%. In addition, the side support rods are made of molybdenum having a higher temperature of recrystallization than that of the cross strap to thereby prevent the weld joint securing the side support rods and the cross straps from completely penetrating through the cross strap.

Further objects and advantages of the invention will become apparent as the following description proceeds 3 and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the invention reference may be had to the accompanying drawings, in which:

FIGURE 1 shows a partially sectioned view of an 'electron discharge device in which the grid structure of this invention has been incorporated;

FIG. 2 shows a side view of a grid electrode structure which has been incorporated in the electron discharge device of FIG. 1; and

FIG. 3 shows an enlarged, sectioned view of the grid structure taken along the line III-III of FIG. 2.

Referring now to the drawings and in particular to FIG. 1, there is shown an electron discharge device employing the present invention in its preferred form. The electron discharge device 10 is comprised of an envelope 12 made of a suitable material such as glass with an electrode assembly indicated generally by the character 24 enclosed therein. The envelope shown is of conventional design and includes a tipped off exhaust 14 on top of the envelope 12 and a button stem header 16 closing off the bottom portion of the envelope 12. A plurality of electrically conductive terminals or lead elements 18 are sealed through the header 16 and are connected to the elements of the electrode assembly 24 by the in terconnecting leads 17. The terminals 18 not only supply the necessary voltage to the elements of the electrode assembly 24, but also act in conjunction with a pair of insulating elements (only element 20 is shown) to support the electrode assembly 24 within the envelope 12.

The electrode assembly 24 includes an electron emissive element or cathode 26 of the indirectly heated type. A folded heater element 34 is disposed within the cathode 26 to energize a layer of a suitable electron emissive material such as one of the barium strontium carbonates. A first anode element 36 and a second anode element (not shown) are disposed on either side of and in planes parallel to the cathode element 26. The anode elements are supported by the spacer elements; more specifically, each of the anode elements has tab portions, one of which is designated by the numeral 38, and which extends through slots 22 within the spacer elements. A control or first grid electrode 29 is disposed about the cathode 26 and is comprised of a pair of side rods 40 which are spaced and rigidly supported from each other by a first and second cross strap 44 and 46 respectively. The first cross strap 44 is secured at one end of the control grid eletcrode 29 while the second cross strap 46 is secured at the other end of the electrode 29 and upon the opposite side of the side support rods 40. More specifically, the cross straps 44 and 46 are secured by welding at those portions of the cross strap designated by the numeral 52. Further, a lateral grid wire 42 made of a suitable material such as tungsten and having a dimeter of approximately .004 inch is wound about that section of the grid electrode 29 between the cross straps 44 and 46. With the frame grid structure as described by this invention, the lateral grid wire 42 may be wound with as many as 300 or 400 turns per inch of the lateral grid wire 42.

As indicated above, there has been a tendency with the structure described above for the cross straps of the grid electrode to fracture. More specifically, when a molybdenum cross strap is welded to the side support rods there is a tendency for the weld to penetrate the entire area designated generally by the character 52 to thereby completely recrystallize the molybdenum structure of the cross straps. Further, it may be understood that those areas designated by the numeral 50 adjacent the spot welds 52 are subject to stress as the lateral grid Wire 42 is being Wound about the side rods 40. It is in these specific areas 50 that fractures are most likely to occur in the cross straps 44 and 46.

Thus, in accordance with the teachings of this invention, the cross straps 44 and 46 are made of a substantially pure molybdenum and in the process of their manufacture are partially recrystallized to a degree in the range of between 20 and In a typical method of manufacture, the ribbon from which the cross straps 44 and 46 is shaped as by a rolling mill to a suitable thickness of about .01 inch. The partial recrystallization of this ribbon is accomplished by standard annealing procedures. Special care must be taken so that the molybdenum does not exceed the temperature limits of recrystallization. The exact temperatures and times of this heating process will vary with the purity of the base molybdenum material. As is well recognized in the art, the previous work done to the base material and the temperature to which the material has been previously heated will determine the exact annealing process. For more complete consideration of these factors, reference is made to the Fabrication of Molybdenum, American Society for Metals, published 1959, pages 1 to 63, and pages 205 to 213.

The molybdenum of which the cross straps 44 and 46 are made should have a purity in excess of 99.9% molybdenum. In one specific example of this material, the cross straps were made of a molybdenum base with the following, additional portions:

Percent Ca .0006 Cu .0004 Fe .0l Pb .008 Mg 0003 Si .005 Sn .02

Referring to FIG. 3, a cross section of the grid electrode of this invention is shown. The side support rod 40,

as explained above, is welded to the cross strap 46 at portion 52 of the cross strap. In a typical method of welding, a pair of welding electrodes are disposed with one electrode at portion 52 of the cross strap 46 with the other electrode disposed on the opposing side upon the side rod 40. The welding electrodes (not shown) are maintained against the side rod and the cross strap under a pressure of approximately 20 to 25 pounds and a current of approximately 2000 to 3000 ampcres with a potential of approximately 3 volts is applied across the electrodes.

A further aspect of this invention involves the material of which the side rods 40 are constructed; more particularly, the side rods 40 should be made of a substantially pure molybdenum having a recrystallization temperature in excess of that of the molybdenum of which the cross straps 44 and 46- are made. The molybdenum of which the side rods 40 is made should have a recrystallization temperature in excess of 900 C. for a ten period. However, a recrystallization temperature slightly in excess of 1100 C. for a ten minute period did provide a more rigid structure. The effect of partially recrystallizing the straps 44 and 46 and of preconditioning the recrystallization temperature of the side rods 40 is shown clearly in FIG. 3. In particular, the Welded regions 56 and 57 of the side rods 40 and the cross strap 46 respectively are of significantly reduced areas. It may be understood that in the welding of unconditioned molybdenum parts that the welding area would have a tendency to penetrate the entire area 52 from the point 50 to the end of the cross strap 46 and would include portions of the side support rod 40. In the portions 57 and 56, the crystalline structure of the molybdenum material is completely recrystallized and tends to be very brittle. Thus, a completely recrystallized cross strap beneath the point designated by the numeral 50 would be subject to fracture either during the winding process or in later use within the envelope of the electron discharge device 10. In accordance with the teachings of this invention, the control of the recrystallization in the cross strap permits lower welding temperatures and currents than are possible with non-recrystallized material. This, in turn, reduces the area in which the welding portions 56 and 57 (as shown in FIG. 3) may extend thus providing a more ductile area at those points where the forces of the lateral grid are applied. The resulting electrode grid structure is therefore more stable when the cross straps are made of a partially recrystallized material and the side rods are made of a material having a high recrystallization temperature.

In one specific example, the side rod 40 is made of a substantially pure molybdenum with remaining portions as follows:

P.p.m. Si 270 Al 75 Fe 25 Mg Pb 10 Sn 10 Cr 10 Co 10 Ni 45 It is noted that the relatively high proportion of silicon is responsible for providing the high recrystalline temperature of the substantially pure molybdenum side rod 40.

This, there has been shown a rigid grid electrode structure which may be manufactured at a significantly reduced cost. Further, the grid electrode structure of this invention will present when incorporated with an electron discharge device a reduced capacitance with respect to the other elements of the device.

While there has been shown and described what is at present considered to be the preferred embodiment of this invention, modifications thereto will readily occur to those skilled in the art. It is not desired, therefore, that the invention be limited to the specific arrangements shown and described and it is intended to cover in the appended claims all such modifications as fall Within the true spirit and scope of the invention.

I claim as my invention:

1. An electrode for an electron discharge device com prising a pair of side support rods disposed in substantially parallel relation with each other, a plurality of lateral grid wires suspended upon said side rods, and first and second cross straps secured at the opposite ends of said side support rods, said pair of side support rods disposed between said first and second cross straps, said first and second cross straps being made of a partially recrystallized material to provide a rigidly strong electrode structure.

2. An electrode for an electron discharge device comprising a pair of side rods disposed in a substantially parallel relation with each other, a plurality of lateral grid wires disposed between and supported upon said side rods, and first and second cross straps secured to said pair of support rods, said pair of side rods disposed between said first and second cross straps with said first cross strap disposed at one end of said pair of side rods and said second cross strap disposed at the opposite end of said side rods, said first and second cross straps being made of a substantially pure molybdenum the crystalline structure of which has been partially recrystallized to a degree in the range of 20 to percent.

3. An electron discharge device comprising an envelope having therein a grid electrode, said grid electrode including a pair of side rods disposed in a substantially parallel relation with each other, a plurality of turns of lateral grid wires disposed about and supported upon said side rods, and first and second cross straps secured to said pair of side rods, said side rods disposed between said first and second cross straps with said first cross strap disposed at one end of said pair of side rods and said second cross strap disposed at the opposite end of said side rods, said first and second cross straps being made of a substantially pure molybdenum whose crystalline structure has been partially recrystallized to a degree in the range of 20 to 80 percent; a cathode element disposed within the opening defined by said pair of side rods and said first and second cross straps; and at least one anode element disposed to receive the electrons emitted by said cathode element, said grid electrode presenting a reduced capacitance with respect to said cathode element and said anode element.

4. An electrode for an electron discharge device comprising a pair of side rods disposed in substantially parallel relation with each other, a plurality of turns of lateral grid wire disposed about and supported upon said side rods, and first and second cross straps secured to said side rods and disposed at the opposite ends of said side rods, said side rods being disposed between said first and second cross straps, said first and second cross straps being made of a material having a purity in excess of 99.9 percent molybdenum and whose crystalline structure has been partially recrystallized to a degree in the range of 20 to 80 percent, said pair of side rods being made of a material having a higher recrystalline temperature than that of said cross straps.

5. An electrode for an electron discharge device comprising a pair of side rods disposed in a substantially parallel relation with each other, a plurality of turns of lateral grid wire disposed about and supported upon said pair of side rods, and first and second cross straps welded upon opposite sides of said side rods, said first and second cross straps being made of molybdenum having a purity in excess of 99.9 percent and whose crystalline structure has been partially recrystallized to an extent in the range of 20 to 80 percent, said side rods being made of a substantially pure molybdenum having a recrystalline temperature higher than that of the molybdenum of which said first and second cross straps is made.

References Cited UNITED STATES PATENTS 3,141,991 7/1964 Vantol et al. 313-350 3,213,313 10/1965 Miale 313-350 3,290,543 12/1966 Weissman 313-346 JOHN W. HUCKERT, Primary Examiner.

A. JAMES, Assistant Examiner.

Images